Steam governing valve apparatus and power generation facility

ABSTRACT

With a simple structure in which the component count is reduced, the occurrence of noise and vibrations can be prevented in a range from a minute opening degree to the vicinity of an intermediate opening degree, and a pressure loss can be decreased when an opening degree is a fully-open opening degree or the vicinity thereof and thus the efficiency of a steam turbine can be improved. A steam governing valve apparatus includes: a valve main body  30  in which a valve chest  31  to which steam is supplied is formed; a valve seat  32  in which a spherical curved surface is formed at a position facing the valve chest  31  that is provided in the valve main body  30 ; a valve element  34  that is housed in the valve chest  31  and on which a spherical curved surface is formed; and a valve rod  33  that is provided on an upstream side relative to the valve element  34  and that drives so that the respective spherical curved surfaces of the valve seat  32  and the valve element  34  contact/separate to set a valve opening degree; in which a bottom portion of the valve element  34  includes a protruding portion  35  that protrudes from a middle position thereof to the valve seat  32  side, and an edge  36  that is formed at a rim so that a recessed portion  37  is formed around the protruding portion  35.

TECHNICAL FIELD

Embodiments of the present invention relate to a steam governing valveapparatus that controls an amount of steam that flows into a steamturbine, and to a power generation facility equipped with the steamgoverning valve apparatus.

BACKGROUND ART

Generally, steam turbines used in power generation facilities such asthermal power plants and nuclear power plants are provided with a steamgoverning valve apparatus on an upstream side of the steam turbine forcontrolling the steam flow rate according to load changes and forcutting off the supply of steam in response to an emergency. The steamgoverning valve apparatus that is arranged upstream of the high-pressureturbine is disposed in series with a main stop valve.

FIG. 14 is an explanatory drawing that illustrates a conventional steamgoverning valve apparatus that is used in a steam turbine. In FIG. 14, amain stop valve 110 that instantly stops steam from flowing into thesteam turbine in response to an emergency or the like with respect tothe steam turbine, and a steam governing valve 120 for controlling asteam flow rate are shown. A side portion of a valve main body 121 ofthe steam governing valve 120 communicates with and is connected to themain stop valve 110. The steam governing valve apparatus has a top cover122 on an upper end portion of the valve main body 121. A valve seat 123that forms a raised shape is provided in an inner portion of the valvemain body 121, and a valve rod 125 that is coupled to a valve element124 that butts against the valve seat 123 penetrates through the topcover 122 and is connected to an oil cylinder 127.

A steam flow from an unshown boiler or the like flows into the main stopvalve 110 as indicated by an arrow I, and flows out from the steamgoverning valve 120 as indicated by an arrow O. When hydraulic pressureacts on the oil cylinder 127 of the steam governing valve 120, the valveelement 124 moves vertically via the valve rod 125, and the steamgoverning valve 120 performs opening/closing operations. The steam flowrate is controlled by the opening/closing operations, and steam flowsinto an unshown steam turbine. Note that, a piston 126 and a closingspring 129 are fitted into the oil cylinder 127 of the steam governingvalve 120, and an oil supply and discharge port 128 is arrangedunderneath the piston 126. A hydraulic device such as a servo valve or adump valve is connected to the oil supply and discharge port 128,although an illustration thereof is omitted from FIG. 14.

Meanwhile, the main stop valve 110 is configured similarly to the steamgoverning valve 120, and has a top cover 112 on an upper end portion ofthe valve main body 111. A valve seat 114 forming a raised shape isprovided in an internal portion of a valve main body 111, and a valveelement 115 that butts against the valve seat 114 is connected to an oilcylinder 117 through a valve rod 116. When hydraulic pressure acts onthe oil cylinder 117, the valve element 115 moves vertically via thevalve rod 116, and the main stop valve 110 performs opening/closingoperations. Supply of steam and cutting off of the supply of steam areexecuted by way of the opening/closing operations. Note that, referencenumeral 113 in FIG. 14 denotes a strainer.

Generally, in a steam governing valve apparatus that is used in a steamturbine of a power generation facility, in particular in the steamgoverning valve 120, unsuitable cases such as the occurrence of noise,vibrations, erosion and material deterioration are known. The steamgoverning valve 120 is configured so as to control the steam flow rateby way of a throttling function between the valve element 124 and thevalve seat 123, that is achieved by moving the valve element 124 in thevalve chest that comprises the valve element 124 and the valve seat 123.It is considered that the aforementioned noise or vibrations arisebecause the noise or vibrations are induced by turbulence in the flow ofsteam around the valve element 124 or an unstable flow or the like (forexample, see Patent Document 1).

Recently, accompanying increases in steam conditions at power generationfacilities (supercritical pressure plants) and increases in the singleunit capacity of steam turbines, improved technology that incorporatesfurther enhancements is being proposed (for example, see PatentDocuments 2 and 3).

As shown in FIG. 15 and FIG. 16, a steam governing valve 120 in theaforementioned Patent Documents 1 and 2 comprises a valve element 124that is formed with a spherical curved surface and has a recessedportion 130 comprising an edge 131 at a rim, and a valve seat 123 thathas a spherical curved surface so as to gradually expand towards adownstream side from a position that the valve element 124 contacts, andis configured so that the spherical curved surfaces of the valve element124 and the valve seat 123 contact each other. Accordingly, in the steamgoverning valve 120, on a bottom portion side of the valve element 124,because the recessed portion 130 having the edge 131 at the rim isprovided, from in a range from a minute opening degree to the vicinityof an intermediate opening degree as shown in FIG. 17(A), a flow ofsteam along the valve element 124 is separated at the edge 131 of thevalve element 124 and becomes a stable flow along the valve seat 123,and thus the generation of noise or vibrations can be prevented.

Further, in a steam governing valve described in Patent Document 3, aflow guide is provided inside a recessed portion of a valve element, andthe flow guide is mounted on the valve main body side.

PRIOR ART DOCUMENTS Patent Documents

Patent Document 1: Japanese Patent Laid-Open No. 56-109955

Patent Document 2: Japanese Patent Laid-Open No. 2006-63957

Patent Document 3: Japanese Patent Laid-Open No. 2008-175267

SUMMARY OF THE INVENTION Problems to be Solved by the Invention

However, the valve element 124 of the steam governing valve 120 inPatent Documents 1 and 2 is a shape that has the recessed portion 130that includes the edge 131 at the rim, and although the configuration iseffective for preventing noise and vibration that is the originalfunction thereof in a range from the start of opening of the valveelement 124 to the vicinity of an intermediate opening degree, in a highvalve opening degree state such as when the valve is in a fully-openopening degree state or in the vicinity thereof as shown in FIG. 17(B),the area immediately below the valve element 124 becomes a dead space,and as shown in by arrows in FIG. 17(B), vortices 132 arise inside thedead space and a pressure loss occurs.

In this connection, with respect to recent steam turbines, there is astrong demand for performance improvement (efficiency improvement) as amarket demand of proprietors of power generation businesses. In terms ofa breakdown of the efficiency of a steam turbine, although improving theinternal efficiency of the steam turbine itself is important, decreasingthe above described pressure loss in the steam governing valve 120 thatis mounted at an inlet of the steam turbine is also extremely important.That is, when a pressure loss arises in the steam governing valve 120 orthe like, it means that the steam pressure at the steam turbine inlet isreduced before doing thermodynamically effective work, and consequentlythe pressure loss has a significant affect (efficiency reduction) on theefficiency of the steam turbine. Therefore, a pending problem for manyyears with respect to the steam governing valve 120 is to what extent itis possible to reduce a pressure loss in a fully-open opening degreestate.

Although the steam governing valve described in Patent Document 3resolves the problem of the dead space directly below the valve elementin the high valve opening degree state by way of a flow guide andsuppresses the occurrence of the vortices 132 to thereby reduce pressureloss, because the flow guide is a separate member from the valveelement, the component count increases and consequently the apparatusstructure is liable to becomes complicated.

An object of an embodiment of the present invention is to provide asteam governing valve apparatus that is made in consideration of theabove described circumstances and that, with a simple structure in whichthe component count is reduced, can prevent the occurrence of noise andvibrations in a range from a minute opening degree to the vicinity of anintermediate opening degree and can reduce a pressure loss when theopening degree is a fully-open opening degree or the vicinity thereofand thus improve the efficiency of a steam turbine, as well as a powergeneration facility that comprises the steam governing valve apparatus.

Means for Solving the Problems

A steam governing valve apparatus according to an embodiment of thepresent invention comprises: a valve main body in which a valve chest isformed to which steam is supplied; a valve seat in which a sphericalcurved surface is formed at a position facing the valve chest that isprovided in the valve main body; a valve element that is housed in thevalve chest and on which a spherical curved surface is formed; and avalve rod that is provided on an upstream side relative to the valveelement and that drives so that the respective spherical curved surfacesof the valve seat and the valve element contact/separate to set a valveopening degree; wherein a bottom portion of the valve element has aprotruding portion that protrudes from a middle position thereof to thevalve seat side, and an edge that is formed at a rim so that a recessedportion is formed around the protruding portion.

Further, a power generation facility according to an embodiment of thepresent invention comprises the steam governing valve apparatusaccording to an embodiment of the present invention.

According to the embodiments described in the foregoing, with a simplestructure in which the component count is reduced, the occurrence ofnoise and vibrations can be prevented in a range from a minute openingdegree to the vicinity of an intermediate opening degree, and a pressureloss can be decreased at a fully-open opening degree or the vicinitythereof to thereby improve the efficiency of a steam turbine.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a system diagram illustrating a power generation facilityequipped with a steam governing valve that is a steam governing valveapparatus according to the present embodiment.

FIG. 2 is a cross-sectional view illustrating a fully-closed openingdegree state in the steam governing valve illustrated in FIG. 1.

FIG. 3 is a cross-sectional view illustrating a minute opening degreestate in the steam governing valve illustrated in FIG. 1.

FIG. 4 is a cross-sectional view illustrating a fully-open openingdegree state in the steam governing valve illustrated in FIG. 1.

FIG. 5 is a multiple view drawing in which (A) is an explanatory drawingfor describing a flow state of steam when the steam governing valveillustrated in FIG. 2 to FIG. 4 is in a minute opening degree state, and(B) is an explanatory drawing for describing a flow state of steam whenthe steam governing valve illustrated in FIG. 2 to FIG. 4 is in afully-open opening degree state.

FIG. 6 is an explanatory drawing for determining a flow channel area ofa steam path portion in the fully-open opening degree state illustratedin FIG. 4.

FIG. 7 is an explanatory drawing for determining a flow channel area ofa steam path portion in the fully-open opening degree state illustratedin FIG. 4.

FIG. 8 is an explanatory drawing for determining a flow channel area ofa steam path portion in the fully-open opening degree state illustratedin FIG. 4.

FIG. 9 is a graph illustrating change characteristics with respect to aflow channel area in the steam governing valve illustrated in FIG. 2 toFIG. 4.

FIG. 10 is a schematic cross-sectional view illustrating dimensions ofrespective members in the steam governing valve illustrated in FIG. 2 toFIG. 4.

FIG. 11 is a graph illustrating a relation between a root diameter Daand an angle THa of a protruding portion and a pressure loss in thesteam governing valve illustrated in FIG. 2 to FIG. 4.

FIG. 12 is a graph illustrating a relation between the angle THa of theprotruding portion and a pressure loss in the steam governing valveillustrated in FIG. 2 to FIG. 4.

FIG. 13 is a multiple view drawing in which (A) is an explanatorydrawing illustrating a flow state of steam when the angle of theprotruding portion is THa=40° in the steam governing valve illustratedin FIG. 2 to FIG. 4, (B) is an explanatory drawing illustrating a flowstate of steam when the angle THa=44°, and (C) is an explanatory drawingillustrating a flow state of steam when the angle THa=60°.

FIG. 14 is a cross-sectional view illustrating a conventional steamgoverning valve apparatus.

FIG. 15 is a cross-sectional view illustrating a fully-closed openingdegree state in the steam governing valve shown in FIG. 14.

FIG. 16 is a cross-sectional view illustrating a fully-open openingdegree state in the steam governing valve shown in FIG. 14.

FIG. 17 is a multiple view drawing in which (A) is an explanatorydrawing of a flow state of steam when the steam governing valveillustrated in FIG. 14 is in a minute opening degree state, and (B) isan explanatory drawing of a flow state of steam when the steam governingvalve illustrated in FIG. 14 is in a fully-open opening degree state.

DESCRIPTION OF EMBODIMENTS

Hereunder, modes for carrying out the present invention are describedbased on the drawings.

FIG. 1 is a system diagram illustrating a power generation facility thatis equipped with a steam governing valve as a steam governing valveapparatus according to the present embodiment. FIG. 2, FIG. 3 and FIG. 4are cross-sectional views that illustrate a fully-closed opening degreestate, a minute opening degree state, and a fully-open opening degreestate, respectively, in the steam governing valve shown in FIG. 1.

In a power generation facility 10 shown in FIG. 1, steam from a boiler11 passes through a main stop valve 12 and a steam governing valve 13 toreach a high-pressure turbine 14 where the steam expands and performswork, and thereafter the steam is once more heated in a reheater of theboiler 11 via a check valve 15, and subsequently flows through a reheatstop valve 16 and an intercept valve 17 and flows in sequence into anintermediate-pressure turbine 18 and a low-pressure turbine 19 andexpands and performs work. After performing work in the low-pressureturbine 19, the steam is returned to water at a steam condenser 20, andthen pressurized by a feedwater pump 21 and supplied again to the boiler11 to be circulated.

Further, in order to raise the operating efficiency of the powergeneration facility 10, depending on the power generation facility 10, ahigh-pressure turbine bypass pipe 22 and a low-pressure turbine bypasspipe 23 are installed so that the boiler 11 can be operated regardlessof the operational state of the turbines 14, 18 and 19. Thehigh-pressure turbine bypass pipe 22 branches from an outlet side of theboiler 11 and is connected to an inlet side of the reheater of boiler11, and includes a high-pressure turbine bypass valve 24. Thelow-pressure turbine bypass pipe 23 branches from an outlet side of thereheater of the boiler 11 and is connected to the inlet side of thesteam condenser 20, and includes a low-pressure turbine bypass valve 25.

As shown in FIG. 2 to FIG. 4, the steam governing valve 13 as a steamgoverning valve apparatus that is mounted in the aforementioned powergeneration facility 10 comprises a valve main body 30 in which a valvechest 31 to which steam is supplied is formed, a valve seat 32 in whicha spherical curved surface is formed at a position facing the valvechest 31 that is provided in the valve main body 30; a valve element 34that is housed in the valve chest 31 and on which a spherical curvedsurface is formed; and a valve rod 33 that is provided on an upstreamside relative to the valve element 34 and that drives so that therespective spherical curved surfaces of the valve seat 32 and the valveelement 34 contact/separate to set a valve opening degree. A bottomportion of the valve element 34 has a protruding portion 35 thatprotrudes from a middle position thereof to the valve seat 32 side, andan edge 36 that is formed at a rim so that a recessed portion 37 isformed around the protruding portion 35. In a state in which the valveopening degree is set to be fully open (hereunder, referred to as“fully-open opening degree”) or a state in which the valve openingdegree is in the vicinity of the fully-open opening degree, a steam pathportion 38 is formed by an inner face of the valve main body 30, thevalve seat 32, the valve element 34 and a guide cylinder 39 that isdescribed later.

That is, a top cover 29 is provided at an upper end portion of the valvemain body 30, and the valve seat 32 is provided inside the valve mainbody 30. The valve rod 33 is coupled to the valve element 34 thatcontacts the valve seat 32, and the valve rod 33 penetrates through thetop cover 29 and is connected to an unshown oil cylinder. When hydraulicpressure acts on the oil cylinder, the valve element 34 moves in thevertical direction in FIG. 2 to FIG. 4 through the valve rod 33. Theguide cylinder 39 that guides the vertical motion of the valve element34 is formed in the top cover 29, and the valve element 34 moves in thevertical direction inside the guide cylinder 39. Note that, althoughbushing is built into a penetrating portion of the valve rod 33 in thetop cover 29 since it serves as a sliding surface of the valve rod 33,illustration thereof is omitted in the present embodiment.

Because the recessed portion 37 that includes the edge 36 at the rim isprovided in the bottom portion of the valve element 34, as shown in FIG.5 (A), in the state of a minute opening degree of the steam governingvalve 13, a flow of steam along the valve element 34 is separated by theedge 36 of the valve element 34 and becomes a stable flow along thevalve seat 32, and hence the occurrence of noise or vibrations isprevented. As shown by an arrow A in FIG. 5(A), since, as describedabove, the flow of steam at such time is an adhering flow along an innercircumferential face of the valve seat 32, a flow is not present alongthe protruding portion 35 of the valve element 34.

As shown in FIG. 2 to FIG. 4, the protruding portion 35 that is providedat a middle position of the bottom portion of the valve element 34 isformed integrally with the valve element 34. In the protruding portion35, a center portion protrudes in a convex shape towards the downstreamvalve seat 32 side, and the protruding portion 35 is defined by adiameter Da of a root portion and an angle THa that are set as describedlater. In addition, a distalmost end of the protruding portion 35 isformed in a substantially hemispherical shape in consideration of safetyduring assembly and the like.

The flow channel area of the steam path portion 38 when the openingdegree is the fully-open opening degree or the vicinity thereof issomewhat larger at an annular portion 38A on an upstream side relativeto the valve seat 32 in comparison to a circular portion 38B on thedownstream valve seat 32 side, and furthermore, as described above,because a swirling flow at a bottom portion of the valve element 34 iseliminated as a result of the protruding portion 35 being formed at thebottom portion of the valve element 34, as shown by arrows B in FIG.5(B), it is easy for steam to flow when the opening degree is thefully-open opening degree or the vicinity thereof.

As described above, when the opening degree is the fully-open openingdegree or the vicinity thereof, the steam path portion 38 is formed bythe inner face of the valve main body 30, the valve seat 32, the valveelement 34 and the guide cylinder 39. The flow channel area of the steampath portion 38 is configured so as to gradually decrease from theannular portion 38A on the upstream side that is defined by the innercircumferential face of the valve main body 30 and the guide cylinder 39towards the circular portion 38B on the downstream side that is definedby the valve seat 32, and to smoothly change in a continuous mannerwithout any extreme changes until ultimately arriving at an opening areaof the valve seat 32 (area that is defined by the inner diameter of thevalve seat 32). Thereby, when the opening degree is the fully-openopening degree or the vicinity thereof, as shown by the arrows B in FIG.5(B), since steam flowing through this steam path portion 38 flowssmoothly without generating a vortex in the vicinity of the bottomportion of the valve element 34, a pressure loss is suppressed.

More specifically, the flow channel area of the steam path portion 38 isconfigured to gradually decrease from the upstream guide cylinder 39 andthe inner circumferential face side of the valve main body 30 towardsthe downstream valve seat 32 side, and is set so as to be smallest at aportion constituted by the valve element 34 and the valve seat 32, andthereafter, while marginally increasing, the flow channel areaultimately arrives at the area that is defined by the inner diameter ofthe valve seat 32. The reason the smallest flow channel area exists atthe portion constituted by the valve element 34 and the valve seat 32 isthat the steam governing valve 13 controls the flow rate of steam atthis portion.

A method for determining the flow channel area of the steam path portion38 (mainly, a portion constituted by the valve element 34 and the valveseat 32) in a fully-open opening degree state will now be describedusing FIG. 6 to FIG. 8.

First, a flow channel area of an inlet portion 42 of the steam pathportion 38 (mainly, a portion constituted by the valve element 34 andthe valve seat 32) is an annular area constituted by an edge endpoint 40of the edge 36 of the valve element 34 and an inlet endpoint 41 of thevalve seat 32. Further, a flow channel area of an outlet portion 43 ofthe steam path portion 38 (mainly, the portion constituted by the valveelement 34 and the valve seat 32) is a circular area defined by an innerdiameter Dth (described later) of the valve seat 32.

Next, a flow channel area partway along the flow path from the inletportion 42 to the outlet portion 43 of the steam path portion 38 isgeometrically determined. A curve 44 that halves the flow channel areafrom the inlet portion 42 to the outlet portion 43 is determined, aperpendicular line (for example, a perpendicular line 45) with respectto the curve 44 is created, and an intersection point (for example, anintersection point 46) between the perpendicular line and the valveelement 34 as well as an intersection point (for example, anintersection point 47) between the perpendicular line and the valve seat32 are determined. When these intersection points are rotated around avalve center line P, a circular truncated cone (for example, a circulartruncated cone 48) is created.

That is, in the steam path portion 38 (mainly, the portion constitutedby the valve element 34 and the valve seat 32), it is assumed that thereare an innumerable number of the circular truncated cones 48 insuccession along the flow direction. An area of a (lateral area) lateralface 51 that excludes an area of an upper bottom face 49 and a lowerbottom face 50 of these circular truncated cones 48 (see FIG. 7) is theflow channel area at the positions of the respective circular truncatedcones 48 of the steam path portion 38 (mainly, the portion constitutedby the valve element 34 and the valve seat 32). When the radius of thelower bottom face 50 in the respective circular truncated cones 48 istaken as R1, the radius of the upper bottom face 49 thereof is taken asR2, and the height thereof is taken as h, the lateral area of eachcircular truncated cone 48 is given by:lateral area of circular truncated cone=π×(R1+R2)×{h ²+(R1−R2)²}^(1/2)

Further, a plurality of circular cones 53, and not circular truncatedcones, are assumed to be present on the downstream side of theprotruding portion 35 of the valve element 34 at the steam path portion38 (mainly, the portion constituted by the valve element 34 and thevalve seat 32). The area (for example, lateral area) of a lateral face55 of the respective circular cones 53 is the flow channel area at thepositions of the respective circular cones 53 of the steam path portion38. When the radius of a bottom face 54 of the respective circular cones53 (see FIG. 8) is taken as R0 and the height is taken as h0, thelateral area of each circular cone 53 is determined by the followingexpression:lateral area of circular cone=π×R0×(h0² +R0²)^(1/2)

A flow channel area at each position of the steam path portion 38(mainly, the portion constituted by the valve element 34 and the valveseat 32) in the fully-open opening degree state is determined asdescribed above. The relation between change characteristics of the flowchannel area of the steam path portion 38 and the valve opening degreeis shown in FIG. 9. In FIG. 9, reference character A0 represents an areaof the inlet portion 42, and reference character L0 represents adistance between the edge endpoint 40 of the edge 36 of the valveelement 34 and the inlet endpoint 41 of the valve seat 32 at the inletportion 42. Further, reference character Ai represents an area thatincludes an arbitrary perpendicular line 45 that is downstream relativeto the inlet portion, and reference character Li represents a distancebetween intersection points 46 and 47 on the arbitrary perpendicularline 45.

In FIG. 9, in a curve X that represents changes in the flow channel areaat a minute opening degree, an angle of inclination in the right-upwarddirection is large, and it is found that at such time the flow channelarea increases and steam separates after passing the edge 36 of thevalve element 34. Further, a curve Y that represents changes in the flowchannel area at the fully-open opening degree exhibits an inclination inright-downward direction, and it is found that at such time the flowchannel area decreases because the protruding portion 35 is formed inthe valve element 34, and steam adheres to the protruding portion 35once the steam is separated by the edge 36. Further, an angle ofinclination of a curve Z that represents changes in the flow channelarea at the intermediate opening degree is small, and it is found thatthe flow channel area at such time is substantially constant, andseparation caused by the edge 36 of the valve element 34 does not occur.

The steam path portion 38 (including the portion constituted by thevalve element 34 and the valve seat 32) is finally determined with theprincipal objective of decreasing pressure loss by defining thefollowing parameters Di, Dth, R, r, Da and THa so as to obtain theoptimal characteristic as represented by the curve Y in FIG. 9 at thefully-open opening degree.

First, as shown in FIG. 10, when a seat diameter that is a diameter ofan osculating circle between the valve element 34 and the valve seat 32is taken as “Do”, a diameter Di of the edge 36 in the recessed portion37 of the valve element 34 is set in a range of:

Do>Di≧0.9 Do,

and an inner diameter (smallest inner diameter) Dth of the valve seat 32is set in a range of:

Di>Dth≧0.8 Do.

Thereby, in a range from a minute opening degree to the vicinity of anintermediate opening degree, steam flowing within the steam path portion38 forms a stable flow along the valve seat 32 (see arrows in FIG. 5),and the occurrence of noise and vibrations is prevented.

Further, when the seat diameter that is the diameter of an osculatingcircle between the valve element 34 and the valve seat 32 is taken as“Do”, a curvature radius R of the valve element 34 is set in a range of:

R=(0.52 to 0.6) Do,

and a curvature radius r of the valve seat 32 is set in a range of:

r≧0.6 Do.

By this also, in a range from a minute opening degree to the vicinity ofan intermediate opening degree, steam flowing within the steam pathportion 38 forms a stable flow along the valve seat 32, and theoccurrence of noise and vibrations is prevented.

In addition, a longitudinal cross-sectional shape of a surface formingthe steam path portion 38 in the protruding portion 35 of the valveelement 34 is defined by a root diameter Da of the protruding portion 35and an angle THa of the protruding portion 35. When the seat diameterthat is the diameter of an osculating circle between the valve element34 and the valve seat 32 is taken as “Do”, the root diameter Da is setin a range of:

Da=(0.40 to 0.44) Do,

and the angle THa of the protruding portion 35 is set to:

THa=30 to 50 deg.

Because the protruding portion 35 is provided in the bottom portion ofthe valve element 34, no unnecessary space is formed within the valvemain body 30, and hence the occurrence of a vortex in the vicinity ofthe upstream side of the valve seat 32 is suppressed. In addition, bysetting the protruding portion 35 within the aforementioned range, theoccurrence of a situation in which the pressure loss increases due tosteam excessively adhering to the protruding portion 35 and causing anincrease in the frictional resistance is prevented.

FIG. 11 shows results obtained when the influence of the root diameterDa and angle THa of the protruding portion 35 on pressure loss wasinvestigated using numerical analysis. In FIG. 11, the horizontal axisrepresents Da/Do and THa, and the vertical axis represents pressureloss. According to the present embodiment, since the root diameter Da ofthe protruding portion 35 is set to 0.40 Do<Da<0.44 Do, as will also beunderstood from FIG. 11, the occurrence of pressure loss is reliablysuppressed. Further, since the angle THa of the protruding portion 35 isset to 30°<THa<50°, as will also be understood from FIG. 11, theoccurrence of pressure loss is reliably suppressed.

To examine in detail the influence of the angle THa of the protrudingportion 35A, numerical analysis was performed in a fully-open openingdegree state in which Da was fixed to the value 0.44 Do. The results areshown in FIG. 12. Vector diagrams of the flow of steam were created tovisually grasp the influence of the angle THa. With respect to thesevector diagrams, a state in which THa=40° is shown in FIG. 13(A), astate in which THa=44° is shown in FIG. 13(B), and a state in whichTHa=60° is shown in FIG. 13(C). In FIG. 13(A), the flow of steam doesnot adhere sufficiently to the protruding portion 35 of the bottomportion of the valve element 34. In FIG. 13(C), the flow is such thatsteam excessively adheres to the protruding portion 35 and consequentlypressure loss increases. The state in which pressure loss is smallest isthe state illustrated in FIG. 13(B), in which the flow of steam is suchthat the steam adheres at just the right amount to the protrudingportion 35.

Because the present embodiment is configured as described above, thefollowing advantageous effects (1) to (4) are obtained according to thepresent embodiment.

(1) As shown in FIG. 2 to FIG. 4, because the recessed portion 37comprising the edge 36 at the rim is provided around the protrudingportion 35 of the bottom portion of the valve element 34, in a rangefrom a minute opening degree to the vicinity of an intermediate openingdegree, a flow of steam along the valve element 34 is separated at theedge 36 of the valve element 34, and the flow becomes a stable flowalong the valve seat 32, and hence the occurrence of noise andvibrations can be prevented.

(2) Because the protruding portion 35 is provided at a middle positionof the bottom portion of the valve element 34, changes in the flowchannel area in the vicinity of the valve element 34 in the steam pathportion 38 when the opening degree is the fully-open opening degree orthe vicinity thereof become small. Consequently, a flow of steam thatflows through the steam path portion 38 does not generate a vortex inthe vicinity of the bottom portion of the valve element 34, andaccordingly a pressure loss is suppressed, and thus the efficiency of asteam turbine can be improved.

(3) The protruding portion 35 is provided at a middle position of thebottom portion of the valve element 34, and the recessed portion 37comprising the edge 36 at the rim is provided around the protrudingportion 35 of the bottom portion of the valve element 34. Therefore, incomparison to a case where the protruding portion 35 and the recessedportion 37 are constituted by separate members, the steam governingvalve 13 can be constituted by a simple structure in which the componentcount is reduced.

(4) For example, with regard to steam turbines in combined-cycle powergeneration facilities, there are many cases in which operation isperformed with the steam governing valve 13 always in a fully-openopening degree state. Meanwhile, according to the steam governing valve13 of the present embodiment, as described in the foregoing (2), theefficiency of a steam turbine can be improved when the opening degree isthe fully-open opening degree or the vicinity thereof. Therefore, byusing the steam governing valve 13 of the present embodiment in ahigh-efficiency power generation facility such as a combined-cycle powergeneration facility, the efficiency of the overall power generationfacility can be improved.

Although an embodiment of the present invention has been describedabove, the present embodiment has been presented by way of example only,and is not intended to limit the scope of the invention. Indeed, thisembodiment may be embodied in a variety of other forms; furthermore,various omissions, substitutions and changes may be made withoutdeparting from the gist of the invention, and such substitutions andchanges are included within the scope and gist of the invention, and arealso included in the scope of the invention described in theaccompanying claims and their equivalents.

The invention claimed is:
 1. A steam governing valve apparatuscomprising: a valve main body in which a valve chest to which steam issupplied is formed; a valve seat in which a spherical curved surface isformed at a position facing the valve chest that is provided in thevalve main body; a valve element that is housed in the valve chest andon which a spherical curved surface is formed; and a valve rod that isprovided on an upstream side relative to the valve element and thatdrives so that the respective spherical curved surfaces of the valveseat and the valve element contact/separate to set a valve openingdegree, wherein a bottom portion of the valve element has a protrudingportion that protrudes from a middle position thereof to a valve seatside and an edge that is formed at a rim so that a recessed portion isformed around the protruding portion, and when a seat diameter betweenthe valve element and the valve seat is taken as “Do”, a root diameterDa of the protruding portion of the valve element is set in a range of:Da=(0.40 to 0.44) Do, and an angle THa of the protruding portion is setin a range of: THa=30 to 50 deg.
 2. The steam governing valve apparatusaccording to claim 1, wherein the protruding portion is formedintegrally with the valve element.
 3. The steam governing valveapparatus according to claim 1, wherein in a steam path portion that isformed by the valve main body, the valve seat and the valve element in astate in which the valve opening degree is set to fully open, a flowchannel area continuously decreases from an upstream side until arrivingat an opening of the valve seat on a downstream side.
 4. The steamgoverning valve apparatus according to claim 1, wherein in a steam pathportion that is formed by the valve main body, the valve seat and thevalve element in a state in which the valve opening degree is set tofully open, a smallest flow channel area exists at a portion that isformed by the valve element and the valve seat.
 5. The steam governingvalve apparatus according to claim 1, wherein a longitudinalcross-sectional shape of a surface forming a steam path portion of theprotruding portion is defined based on a diameter of a root portion andan angle.
 6. The steam governing valve apparatus according to claim 1,wherein, in the protruding portion, a center portion protrudes in aconvex shape towards a downstream valve seat side, and a distalmost endis formed in a substantially hemispherical shape.
 7. The steam governingvalve apparatus according to claim 1, wherein a diameter Di of an edgeof the valve element is set in a range of: Do>Di≧0.9 Do, and an innerdiameter Dth of the valve seat is set in a range of: Di>Dth≧0.8 Do. 8.The steam governing valve apparatus according to claim 1, wherein acurvature radius R of the valve element is set in a range of: R=(0.52 to0.6) Do, and a curvature radius r of the valve seat is set in a rangeof: r≧0.6 Do.
 9. A power generation facility that comprises the steamgoverning valve apparatus according to claim 1.